a. Field of Invention
The invention relates generally to pivotable closure assemblies, such as tailgates, for pick up trucks, SUVs and other such vehicles, and more particularly, to a tailgate assembly which is capable of being opened and closed in an assisted manner and with a controlled velocity.
b. Description of Related Art
As is known in the art, pick up trucks, SUVs and other such vehicles generally include a tailgate having a variety of components for facilitating or limiting movement of the tailgate. For example, referring to FIGS. 1 and 2, a typical pick up truck 10 is illustrated including a tailgate 12 whose movement in the tailgate opening direction is controlled by tailgate pivot brackets 14. For conventional tailgates such as tailgate 12 of FIGS. 1 and 2, when the tailgate is moved from its closed position of FIG. 1 to its open position of FIG. 2, the tailgate generally pivots open under the force of gravity or with limited resistance by a torsion rod until pivotal movement thereof is stopped by brackets or cables 14. As readily evident, this pivotal movement is generally uncontrolled as the tailgate abruptly stops upon reaching its open horizontal position of FIG. 2. If the tailgate is inadvertently left in this open position during movement of the vehicle, the tailgate may bounce uncontrolled and thus prematurely damage the tailgate or its associated components.
Likewise, when tailgate 12 is moved from its open position of FIG. 2 to its closed position of FIG. 1, a user can often lift the tailgate with a force sufficient to lift the tailgate but insufficient for fully engage the tailgate's latching mechanism, thus requiring a second attempt to fully latch the tailgate. This is generally because the user must first lift the tailgate from its horizontal resting position, and once the tailgate is in motion, the user applies a lesser force to the tailgate as the force required to continue the closing motion is less than the initial force required to lift the tailgate.
In an effort to address the aforementioned drawbacks of conventional tailgates, a variety of mechanisms have been proposed for assisting with the tailgate closing function, as well as for controlling the tailgate opening velocity.
One such exemplary design for assisting with the tailgate closing function is disclosed in U.S. Pat. No. 6,773,047 to Gruber. Specifically, referring to FIGS. 4 and 5 of Gruber, there disclosed a vehicle tailgate lift system including an energy storage device (10) located within a vehicle body adjacent the D-pillar and pivotally anchored to the vehicle body. A bellcrank arm (13) is pivotally attached to energy storage device (10) and rigidly attached to an actuation shaft (14; see FIG. 2) that is coaxially aligned with tailgate (2) and its pivot axis. As tailgate (2) is moved from its open position of FIG. 4 to its closed position of FIGS. 1 and 5, stored energy in device (10) at the tailgate open position is released to assist with the tailgate closing function.
While the tailgate lift system of Gruber provides adequate lift assistance, the mechanism nevertheless has several drawbacks related to packaging, operation and adjustability thereof. For example, referring to FIGS. 4 and 5 of Gruber, the Gruber tailgate lift system includes a relatively long energy storage device (10) and similarly long bellcrank arm (13) for generating an adequate moment for rotating tailgate (2), with device (10) being pivotally mounted to the side wall in the D-pillar area. As readily evident, the size of device (10) and bellcrank arm (13) require these components to be installed in the D-pillar area, which is itself limited in space due to the structural rigidity and performance requirements for this area. Since energy storage device (10) provides the primary force for assisting with movement of tailgate (2), adjustability in the opening or closing movement of tailgate (2) is limited to the operational parameters of device (10), which as discussed above, can itself in conjunction with bellcrank arm (13) be a design drawback due to the large size thereof.
Another exemplary design for assisting with a tailgate opening/closing function is disclosed in U.S. Pat. No. 5,271,652 to Watanabe. Specifically, referring to FIGS. 1-3 of Watanabe, there disclosed a device for applying an auxiliary force to a loading deck side plate (13). The device includes a spring (20) for pulling rod (21) attached to an intermediate link (25), with link (25) being connected to a swing link (16) connected to side plate (13). As with the lift assist device of Gruber, while the Watanabe device functions to assist with the opening and closing of side plate (13), the device nevertheless is incapable of a smooth opening/closing operation due to the fact that swing link (16) abruptly rotates during opening or closing of side plate (13) as illustrated in the FIGS. 1-3, and is therefore undesirable for use as a tailgate assist device.
Yet further, another exemplary design for assisting with a tailgate opening/closing function is disclosed in U.S. Pat. No. 3,883,014 to Glomski. As illustrated in FIGS. 1 and 2 of Glomski, there is disclosed a tailgate lift mechanism including cylinder (39) for actuating piston rod (40) to drive bell crank levers (42-44), which in turn drive tie rod (45) to further drive pivot links (45), which yet further drive lift arms (30) to lift the tailgate. As readily evident, the interaction and operation of the several links for Glomski render the tailgate mechanism thereof susceptible to premature malfunction, and further, the mechanism is generally required to be installed below vehicle bed (19) due to the several linkages required for adequate operation.
It is therefore desirable to provide a vehicle tailgate movement assist mechanism which may be installed adjacent the vehicle D-pillar, or along the width of the vehicle bed, without significantly impacting the space required for other structural components, or without being visible to a user. It is also desirable to provide a vehicle tailgate movement assist mechanism which is capable of being readily tuned and adjusted to a user's operational parameters, which includes a minimal number of components for thus simplifying the manufacturing and assembly steps required for such components, and which provides a smooth opening or closing assist operation.